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Forum Index : Solar : Do you really need a big system?
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yahoo2 Guru  Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Funnily enough what I am saying applies to grid systems too. there are two feed in tariffs the retailers and distributors tariff if you accept the money from the distributors tariff you have to restrict your output to the "approved peak capacity" on a standard single phase connection you are allowed a 5 kw inverter and the equivalent output of 6.5 kw of north facing panels. this does not apply if you take the retailers tariff only. it is up to the retailer how much they let you produce. These phantom loads eat into a systems production during the day and increase the nightly grid bill. fridges with icemakers that cant be switched off defrost elements that automatically run at night satellite decoders that power the dish low noise block at 18 volts air conditioner control panels that chew power water pumps with huge start up power loads and broken accumulators. solar water heaters that run the boost element every time a tap is turned on because the water pressure is mixing the cold water with the hot. the new computer I am fitting soon runs two 27 inch screens for a total less than 50 watts and it drops to less than half a watt the second I walk away. I run three micro servers at 5-10 watts a piece. compare the power usage of a dual plate grill, a microwave steamer, a benchtop convection oven, a pressure cooker, a slow cooker, an air fryer. all of these smash a conventional oven and stove for efficiency just because of less heat loss. I helped someone modify the thermal layer of their house this summer, we haven't done a final costing on it yet but their A/C has only run on four occasions since. Runs for about 12-15 minutes then stops for an hour (about 50 watts). Before the revamp they were chewing 900-1300watts/ hour probably 2-3 afternoons and evenings a week to cool the house. I'm confused, no wait... maybe I'm not... |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Have to agree, there is often a lot more going on at night than is really necessary. I found to my horror that my garage door opener has a huge step down transformer and rectifier to power the dc motor. This transformer drew a constant 36 watts of idling power, and it ran extremely warm.... to power the radio receiver. So what I did was power just the small radio receiver from a switched mode 12v dc wall pack. When I push the button to open or close the garage door, a relay feeds 230v to the big transformer, and the whole thing operates completely normally. It cost me almost nothing to do this modification. Once the problems are identified, a bit of inginuity and sneakiness can result in significant savings with minimum expense to do it. And its fun and a challenge. Cheers, Tony. |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
I've been told on more than a few occasions my battery bank is too small, but I've never really had any issues, in that I've never run out of power and the batteries have lasted 5 years. I do cut back on power use at night though, just the water pump, fridge, tv, computer, lights, kettle and microwave. During the day is another story, I waste power. I am lucky though, I live alone so I can make a few sacrifices as/when needed and I'm ok with that. If its been an overcast few days, that night I go into economy mode, I'll use gas for boiling the kettle, keep the nightly shower short and shut down the computer unless I'm using it. TV and lights etc still on. I'm only drawing 200 watts. My batteries do OK, the last set lasted just over 5 years and they only cost $1600 to replace. So at this stage I dont really need a bigger bank. If I ever do find a tolerant woman who actually wants to move in with me, then things may change a little. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I look at this another way.... All of these things mentioned either wouldn't be suitable for my familiy's lifestyle or we don't own the things... probably because of reason 1. I don't know what they are worth but I would think that if you bought 2 you could expect them to average out at $100 ea. If I bought $200 worth of used panels, I'd be getting 2-3Kw worth on what I have been paying. From that say 2 KW I could expect to get an average of 3 KW per day min standing on my head where I am even if I face them west at the less than ideal angle. The normally attributed return is 4.5x for an ideal orientation. But just to play safe I'll call it 3 Kwh day average. To me the question is, will purchasing the more efficient appliances save me more money than doing/ using what I have and putting the money I'd spend on new appliances on 2 Kw worth of panels? For ME, it's a no brainer. The panels will win by a country mile. We eat out twice a week to start with so there is an extra 6KWh up our sleeves to start with. In the warmer months we cook maybe 2 nights a week and eat cold food or BBQ the others so there is another bunch of Kwh in the kitty to squander on the inefficient appliances. I would also expect even the used panels to outlast the appliances as well so there would be a cost saving right there or, in X number of years I could go buy another 2Kw of panels. Obviously then there is no comparison because the cost of power has most likley gone up as well and the margins increased. Also has to be remembered that it's not the total amount of power they use, only the difference in what a more efficient appliance would use and the extra the ones we have now would consume, not the whole amount. I can't see that margin being more than a KWh or 2 on any meal and I think that's being real generous. Battery or grid, for my home and many others, especially the 1-2 person households, I reckon spending more on panels would yield vastly more savings than buying more efficient appliance that are used occasionally like those mentioned. Fridge and other 24/7 things used many hours per day may be different but the cooking appliances, I'll put my money into panels and put the excess which they will surely generate into other comforts or savings. I am not dismissing the idea of more efficient appliances/ methods, I do understand some people want to satisfy that niggling feeling to do what they think is the best ways. I can certainly relate to that, god knows I have enough hangups and proclivities to understand it real well in the way I don't feel content unless some things are done the way I want them. Just trying to point out that savings and efficiency do have more than one way of being looked at and it's not always doing things the best way that yields the best results. |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
My thoughts on this would be to run a small battery bank and a LOT of panels. Like some here already do, size for the overcast crappy days so you have power no matter what. As also said, batteries are the exy part, panels are cheap as chips now. I would also say one would get a lifetime of service from an old lister or a Chinese Horozontal on a generator when used the Week? a year when the panels couldn't keep up or to take the drain off the batteries with heavier loads. If I were trying to set up a battery bank, through he day I'd want things running off the power the array was generating without touching the batteries at all and with enough overhead to be charging them as well. If I had to fire the genny so the battery's aren't touched, still good. I did this with my play/ learning/ experimental setup and it worked very well. Put enough over head on it so I could still boil the electric jug at 4 in the afternoon and not touch the batteries ( 2x Car batteries) at all. Seems to me a lot of offgridders have this thing about a lot of storage and go to a lot more expense than firing up the Genny on the occasions they need it could ever cost. I would really only need the batteries to get me through from 5pm to 7 am. Rest of the time I would fire a veg fuelled Genny to keep the batteries topped up and take the rest of the load direct as it were. |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
If you are using lead acid batteries there lifespan is greatly reduced if you regularly discharge more than 20%. The 775AH battery I have just gives us that 20% drawdown overnight but on occasion, we have gone down to 50%. It is a forklift battery and they are supposed to be able to do 80% discharge every day. Now I have 14KW of panels it is only on the really cloudiest of days that we don't get a full charge. I had dreams of having enough solar to get through any weather but that is not realistic where we are near the coast and the heavy cloud cover we can get. So a backup power source is a must, I figure that maybe 10 days a year that would be required. We are in the process of buying a property which has a big benefit for off-grid especially in rainy weather, the photo shows 12 metres of the total fall of 75 metres available.  There are only 10 types of people in the world: those who understand binary, and those who don't. |
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Clockmanfr Guru Joined: 23/10/2015 Location: FrancePosts: 429 |
Elephant in the room !!!! AC coupling. I use and obtain of fleebay cheap GTI's with MPPT and they are processing 15kW of my PV. They are connected to the OzInverter created Mini Grid. So in essence the GTI's are feeding my AC 230v mini grid needs, and also back charging the 48vdc 1300ah SLA batteries, Oztules battery concept.. Each of my GTI's has a shut down simple circuit when the batteries reach a particular charged state. I have the GTI's shutting down sequentially with a time hysteresis. I have 7 independent buildings, PV arrays on roofs/static etc, 4 separate dwellings, so my system is not small. BUT and a great fantastic BUT... I do not need to install a bigger battery bank and have more of that expensive DC MPPT charging controller /regulators etc . I have 5kW of PV on trackers, what a pain dealing with that 150v dc cabling and controls. So AC Coupling is the way forward. And another bonus with the Mono PV is that in ambient light, ie murky conditions, I am still getting 15% to 25% of that 15kW, so that's about 1.5kw coming into my mini grid. Who needs a big battery bank and expensive MPPT DC controllers.?????? Everything is possible, just give me time. 3 HughP's 3.7m Wind T's (14 years). 5kW PV on 3 Trackers, (10 yrs). 21kW PV AC coupled SH GTI's. OzInverter created Grid. 1300ah 48v. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
My latest approach to all of this is to design a new inverter that will work directly from the solar panels during the day, without requiring any connection at all to a battery to stabilise the inverter input voltage. Grid tie inverters work that way, and so could a straight off grid inverter if it can handle large and sudden voltage swings to the dc input voltage. I am now also becoming one of the big solar / small battery believers. It does require a lot of solar panels, which these days is not such a problem, plus an inverter design that voltage regulates over an usually wide input voltage range. (2:1 input voltage range) That by itself should cover all my normal daytime loads, except for some very short periods on the worst cloudy days. A battery is obviously still required at night, but it slowly charges continuously throughout the whole day, and then slowly discharges at night. There will be only one long continuous charge cycle, then one discharge cycle every 24 hours. That is much more gentle to the battery than having very high currents alternately shuffling in and out of the battery throughout the day, with a large number of mini charge/discharge cycles. It should also be possible to reach a higher final state of charge if there are no short high current discharges during the charging process. Cheers, Tony. |
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| Clockmanfr Guru Joined: 23/10/2015 Location: FrancePosts: 429 |
Hi Tony, I have been singing your concept to a few folk on this side of the planet, about your inverter concept that does not need a stable HZ and correct voltage reference. So we look forward to your endeavours. For me its always cost effectiveness, and those second hand GTI's are just so cheap. Just got 3 off SMA SB 1700w (torroid type) for $50 each. And at present good quality PV is so so cost effective. Everything is possible, just give me time. 3 HughP's 3.7m Wind T's (14 years). 5kW PV on 3 Trackers, (10 yrs). 21kW PV AC coupled SH GTI's. OzInverter created Grid. 1300ah 48v. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
The boards that I am making will do what you want Yahoo with a battery bank, much the same as Clockman except in my case I will have control over the charge current. So the charge controller will use PWM to reduce the power available to GTI's based on battery voltage and charge current. It won't matter what AC loads you have running as the battery current is what is being controlled. If the sun is shining bright and you have the AC, HWS, oven etc running the GTI's will power them and the leftover power that is going to the battery via the Inverter is limited to the set current. I am doing this now except for the current limiting which I am working on ATM. There will be the possibility of turning on the HWS and similar loads when the regulator starts to throttle back the GTIs, ie if PWM =< 80% pin 4 = HIGH & if PWM == 100% pin 4 = LOW. The threshold for this would need to be set to suit the amount of PV being used. You could also have circuits that are turned off when the power input reduces the charge current to help avoid any discharge during the day. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Clockmanfr Guru Joined: 23/10/2015 Location: FrancePosts: 429 |
Hay Madness, that's a fantastic sexy waterfall you have there. wow! Everything is possible, just give me time. 3 HughP's 3.7m Wind T's (14 years). 5kW PV on 3 Trackers, (10 yrs). 21kW PV AC coupled SH GTI's. OzInverter created Grid. 1300ah 48v. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Yes I like it, there are a few others but that is the best one. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Clockman, my ideas are still slowly formulating and evolving, but I now have a driver board completed and tested, but have not started on the power stage yet.Just have some constant amplitude sine waves to look at on a CRO. The same concept could work with either PWM or my stepped sinewave method. The "trick" is that it requires no voltage feedback from the output, which gets around a lot of the speed of response, and stability issues associated with PID control. What it does it constantly measures the inverter dc input voltage, and generate a constant amplitude sine wave drive for the output transformer from that. Its very fast acting as each cycle is uniquely generated from the measured dc input voltage. The microprocessor derived waveforms can keep the transformer primary ac voltage constant regardless of very sudden output load jumps, or input voltage changes. Its works very well with the very poorly regulated direct output from a solar panel current source. There is only a very slight reduction in voltage regulation due to the transformer itself, but even the grid voltage wanders around a bit, and it should be much better than that. Like most of the things I fiddle around with here, its all a bit unusual and pretty unique. Its much more interesting and challenging to come up with something totally original that nobody else has, especially when its proven to work. Cheers, Tony. |
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| Clockmanfr Guru Joined: 23/10/2015 Location: FrancePosts: 429 |
Yes , I have been reading your thread. And it does look like you have a concept that will function as you require. Real neat if you can get it to compensate for loadings quick enough to not spook a standard GTI required internal references. Carry on your unique Fiddling.! Everything is possible, just give me time. 3 HughP's 3.7m Wind T's (14 years). 5kW PV on 3 Trackers, (10 yrs). 21kW PV AC coupled SH GTI's. OzInverter created Grid. 1300ah 48v. |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I sometimes troll the Real estate sites for properties like this. To me MH is the ultimate power source. 24/7, stable and comes with other benefits. I'd love just a small block not too far away to set up a weekender from shipping containers and go from there. A car alternator of modest size will do 1 Kw. 24Kwh a day. You need a fair bit of solar to do that and even as cheap as I buy it, still way more exy than a used alternator.... which I can get as many as I want for nothing. I think a lot of people underestimate the life of the humble car alternator and the efficiency. If you look at the mileage they do in vehicle and convert that to hours running time, they are impressive. I'd get a bunch of the alts, set them up with a much more efficent external alt that are made for battery charging and have variable outputs from the same alt and run them till they fell over. Then I'd Put in new bearings and bushes and get years more service out the things. Set up 3 and run 1-2 and have one redundant for backup when needed. Simple and easy to make goo reliable power. Care to Divulge what area you found this place mad? Most of what I have seen suitable is northern NSW and up or south towards or in Vic. Have seen a few places inland in the hill from where my father is in Taree as well. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
George the property is in the Sunshine Coast Hinterland in SE QLD. Took me a while to find this place and I am a Real Estate Agent. The flow over the waterfall is after a few months of good rain, after heavy rain there is massive amounts of water that goes down that creek. In drier times though it never stops but slows down to a trickle. It is not suitable for 24/7/365 hydro however I plan to build a dam near another small creek up the top. I will then be able to use excess solar power to pump up to the dam during the day and run hydro at night. Getting 1 KW continuos at the head I have available would require a flow of 2 litres per second using a more efficient motor from a F&P washer. This will supply high voltage DC to the house about 400M away where I will connect it to a GTI. I will be aiming for around 750W going bigger requires pipe bigger than 50mm which starts getting very expensive very quickly with the pressure involved. With this setup and the dam I am planning I could get about 2 weeks running from a full dam, it will eliminate most of the draw on the battery. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
Sounds Brilliant. 2 week capacity pure water battery. Every home should have one! Sure beat the hell out of one of those silly tesla batteries. Brilliance of this is when the solar is not producing much through the day it will probably be raining when means the hydro will be working. I was just up on the Gold Coast over Easter and into the first week of the games. Rained every single day and some of the downpours at night were torrential. I traded an F&P motor last weekend for an IBC tank. want to set it up and have a play with driving it off one of my little Diesels. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
That is 2 weeks with 0 solar which won't happen (I hope), I would not want to drain it completely anyway. I would not be so hard on the Tesla battery it might not be cost-effective ATM but it is causing a shift towards batteries for everyone. I am sure if a couple fell off the back of a truck at your place they would be up on the wall very quickly. You get f all for exporting power so why not store and use it at tnight. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| ryanm Senior Member  Joined: 25/09/2015 Location: AustraliaPosts: 202 |
Super jealous of your new place Madness. Would looove to have a micro hydro setup myself, but a combination of flat and dry makes it unlikely. Lots of really good info over at builtitsolar . |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Good news Ryan is that solar will work better for you, we get periods of really thick cloud that reduces solar output to about 10%. I am going to use a Pelton AFIK they are the most efficient at higher heads. I also plan to rebuild a Dunlite Wind Generator I have also and use that because I can. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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